The present invention relates to a quartz oscillator device in which a quartz oscillating plate is held attached with the use of a silicone-based conductive adhesive.
With regard to quartz oscillators such as quartz oscillators and quartz generators, the surface-mount oscillator which employs a ceramic package has come to occupy a dominant share. Moreover, in order to cope with the trend of micro-miniaturization, more and more surface-mount oscillators are arranged to support the quartz oscillating plate without an elastic metal support. Where an elastic support is omitted, the quartz oscillating plate is frequently fixed in the ceramic package with the use of a silicone-based conductive adhesive in order to ensure the impact resistance. The silicone-based conductive adhesive is obtained, for example, by adding a silicone resin-based adhesive with a conductive filler. The silicone-based conductive adhesive, which keeps its flexibility after curing, is superior in alleviating an external stress acting on the quartz oscillating plate.
As a conventional example, a surface-mount oscillator is mentioned with reference to FIG. 13. This surface-mount quartz oscillator comprises a ceramic package 7 whose external configuration is a near rectangular solid and which includes a recess opening at the top, a rectangular quartz oscillating plate 8 which is housed in the ceramic package 7 as a piezoelectric oscillating component, and a metal lid 9 which is bonded at the opening of the ceramic package 7.
The ceramic package 7 is composed of a ceramic body 70 with a recess and a metal layer 71 which is provided along the top surface of the peripheral wall 701 of the ceramic body 70. The metal layer 71 is composed of a metallized layer of tungsten, etc., and a Ni-plated layer and an ultrathin Au-plated layer successively laminated on the metallized layer. On the internal bottom surface of the ceramic package 7, two electrode pad layers 72 are provided in the direction of short sides (only one such pad is shown). The electrode pads 72 are electrically guided out to the external bottom surface of the package, via connection electrodes 73, by lead electrodes 74, 75, respectively.
The rectangular quartz oscillating plate 8 is cantilevered at one longitudinal end by these two electrode pads 72. The quartz oscillating plate is formed with a pair of excitation electrodes 81, 82 on the front and back surfaces. These excitation electrodes 81, 82 are led out to the sections of the electrode pads 72 and electrically connected therewith by a silicone-based conductive adhesive 300. Each of the excitation electrodes 81, 82 is composed of a Cr film layer and a Au film layer which are laminated in this order by sputtering or vacuum evaporation. In addition, the metal lid 9 is brazed and soldered on the top surface of the metal layer 71 with a silver brazing material 400, whereby hermetic sealing is established.
However, the silicone-based conductive adhesive shows a weak adhesion strength with respect to the Au surface, which may increase the conductive resistance and also cause breakage of the adhesion surface. Considering the Au at the surface does not go through an oxidation reaction and remains stable, the decrease in adhesion strength is presumably because the Au is difficult to bond chemically to the silicone-based conductive adhesive.
In particular, where the quartz oscillating plate is cantilevered, the weight of support or the weight of impact is focused so heavily on the adhesion area as to induce occurrences of breakage. In recent arrangements designed for low-profile devices, the adhesive is applied only on the adhesion surface of the quartz oscillating plate, and not on the top surface thereof. This arrangement has also resulted in deterioration of the adhesion strength.
To compensate for the decreased adhesion strength, prior art (e.g. Japanese Patent Laid-open Publication Nos. H3-190410 and H7-283683) has devised to raise the adhesion strength by applying an adhesive on the base part of the quartz oscillating plate, or by exposing the ceramic base part of the ceramic package (as the base) and applying an adhesive on the exposed base part.
In the recent situation, miniaturization of the quartz oscillator device not only demands a smaller quartz oscillating plate but also allows a less area for lead electrodes. In this respect, if the size of lead electrodes is diminished in the above prior art, the CI (crystal impedance) varies seriously relative to the change of the drive level.
The present invention has been made to solve these problems, with an intention of providing a quartz oscillator device in which the quartz oscillating plate is bonded to the electrode pads on the base by means of a silicone-based conductive adhesive, which device can maintain a good adhesion state and adhesion strength, which can show a remarkable impact resistance, and which can facilitate frequency adjustment in the later step.
In order to solve the above problems, the present invention discloses a structure in which a suitable easily oxidizable metal is provided very thinly at least either on the metal film defining the surface of each lead electrode formed on the quartz oscillating plate or on the metal film defining the surface of each electrode pad formed on the base, so that the quartz oscillating plate and the electrode pads can be bonded by a silicone-based conductive adhesive. This structure is realized by the following arrangements.
A quartz oscillator device corresponding to claim 1 comprises a quartz oscillating plate having two major surfaces, each of which is formed with an excitation electrode and lead electrodes drawn out of the excitation electrode, and electrode pads formed on a base, wherein the quartz oscillating plate and the electrode pads are electrically connected via a silicone-based conductive adhesive. This quartz oscillator device is characterized in that, among the excitation electrode and the lead electrodes, at least each of the lead electrodes comprises a Cr film layer, a Au film layer, and a thin Cr film layer or a thin Ag film layer, which are laminated on the quartz oscillating plate in this order.
In the arrangement of claim 1, a thin Cr film layer or a thin Ag film layer is formed as the uppermost layer of each lead electrode. As a result, when the silicone-based conductive adhesive is employed, not only does the relatively easily oxidizable Cr or Ag improve the adhesion strength, but also the Au film ensures good conductivity.
A quartz oscillator device corresponding to claim 2 comprises a quartz oscillating plate having two major surfaces, each of which is formed with an excitation electrode and lead electrodes drawn out of the excitation electrode, and electrode pads formed on a base, wherein the quartz oscillating plate and the electrode pads are electrically connected via a silicone-based conductive adhesive. This quartz oscillator device is characterized in that each electrode pad comprises a metallized layer made of tungsten or molybdenum, a Ni film layer and a Au film layer, which are laminated on the base in this order; and that Ni in the Ni film layer is diffused at least into a predetermined area of the Au film layer in each electrode pad where the silicone-based conductive adhesive is applied.
The arrangement of claim 2, in which Ni is diffused into the uppermost Au film layer in the electrode pad, can enhance the adhesion strength by the silicone-based conductive adhesive, without increasing the overall film thickness of the electrode pad. Notably, such diffusion is accomplished by a rather simple heat treatment.
A quartz oscillator device corresponding to claim 3 comprises a quartz oscillating plate having two major surfaces, each of which is formed with an excitation electrode and lead electrodes drawn out of the excitation electrode, and electrode pads formed on a base, wherein the quartz oscillating plate and the electrode pads are electrically connected via a silicone-based conductive adhesive. This quartz oscillator device is characterized in that each electrode pad comprises a metallized layer made of tungsten or molybdenum, a Ni film layer, a Au film layer, and a thin Ag film layer or a thin Al film layer, which are laminated on the base in this order.
In the arrangement of claim 3, a thin Ag film layer or a thin Al film layer, formed as the uppermost layer of the electrode pad, increases the thickness of the electrode pad. Nevertheless, this arrangement can enhance the adhesion strength to the silicone-based conductive adhesive, in comparison with the case where the uppermost layer is a Au film layer.
The quartz oscillator device according to claim 2 or 3 may be arranged such that, among the excitation electrode and the lead electrodes, at least each of the lead electrodes comprises a Cr film layer, a Au film layer, and a thin Cr film layer or a thin Ag film layer, which are laminated on the quartz oscillating plate in this order.
According to this arrangement, the uppermost layers of the lead electrodes and those of the electrode pads both comprise not only Au but also a relatively easily oxidizable metal such as Cr, Ag, Al or Ni. As a result, the lead electrodes and the electrode pads can bond well to the silicone-based conductive adhesive, with an increased adhesion strength.
A quartz oscillator device corresponding to claim 5 comprises a quartz oscillating plate having two major surfaces, each of which is formed with an excitation electrode and lead electrodes drawn out of the excitation electrode, and electrode pads formed on a base, wherein the quartz oscillating plate and the electrode pads are electrically connected via a silicone-based conductive adhesive. This quartz oscillator device is characterized in that each of the excitation electrode and the lead electrodes comprises a Cr film layer and a Au film layer, which are laminated on the quartz oscillating plate in this order; and that, among the lead electrodes and the excitation electrode which are opposite to the base, at least each of the lead electrodes comprises a thin Cr film layer or a thin Ag film layer which is laminated on the Au film layer of the lead electrode.
According to claim 5, among the lead electrodes and the excitation electrode which are opposite to the base, at least each of the lead electrodes includes a thin Cr film layer or a thin Ag film layer which is laminated as the uppermost layer. As a result, not only does the relatively easily oxidizable Cr or Ag improve the adhesion strength, but also the Au film ensures good conductivity.
In addition, the Cr film locates only on the back surface of the quartz oscillating plate, i.e. on the side of the electrode pad formed on the base, whereas no Cr film is present on the front surface of the quartz oscillating plate. Consequently, frequency adjustment is efficiently conducted with respect to the Au film on the front surface, and better electrical characteristics are obtained.
The structure of claim 5 may be arranged as recited in claim 6. In this case, each electrode pad may comprise a metallized layer made of tungsten or molybdenum, a Ni film layer and a Au film layer, which are laminated on the base in this order; and Ni in the Ni film layer may be diffused at least into a predetermined area of the Au film layer in each electrode pad where the silicone-based conductive adhesive is applied.
Alternatively, as recited in claim 7, each electrode pad may comprise a metallized layer made of tungsten or molybdenum, a Ni film layer, a Au film layer, and a thin Ag film layer or a thin Al film layer, which are laminated on the base in this order.
Preferably, the thin Cr film layer or the thin Ag film layer has a thickness of 5 to 50 xc3x85.
As for the uppermost layer of each lead electrode or the excitation electrode (i.e. the thin Cr film layer or the thin Ag film layer), a thin film layer with a film thickness is 5 xc3x85 or less fails to exhibit the intended effect, and, as a consequence, the adhesion strength is lowered. On the other hand, where the thickness is over 50 xc3x85, the quartz oscillator device shows such a high CI that the oscillation characteristics are adversely affected. In view of these facts, the thin Cr film layer or the thin Ag film layer, as the uppermost layer, should have a thickness in the above-specified range, thereby to enhance the impact resistance and to keep the CI and other electrical characteristics in good conditions.
Further, a quartz oscillator device corresponding to claim 9 may be arranged such that the lead electrodes formed on both major surfaces of the quartz oscillating plate are different from each other in shape or size of the electrode pattern.
This arrangement facilitates the distinction of the front surface and back surface of the quartz oscillating plate which is equipped with these electrodes. To give an example, in order to impart favorable electrical characteristics to the quartz oscillator, the back surface is preferably formed with a thin uppermost Cr film. In this case, it is often difficult to judge the presence or the absence of the Cr film by visual inspection or the image processing technology using a digital camera or the like. However, according to the arrangement of claim 9, such judgement can be made apparently. Besides, with regard to the production utilizing an automated machine, etc., this arrangement can work efficiently and raise a production yield.